Current clinical and pathological data suggest an ongoing major shift in the mechanisms of the thrombotic complications of human atherosclerosis. Human plaques contain less lipid and fewer macrophages in the statin era. Patients with acute coronary syndromes (ACS) include more and younger women, and obese and insulin resistant individuals. ST segment elevation myocardial infarctions (STEMIs) have declined as non-STEMIs have risen. We have marshaled evidence for a shift in the mechanisms of ACS. In the current era of intense LDL lowering, rupture of so-called ?vulnerable plaques? now causes fewer acute coronary syndromes while superficial erosion is increasing as a proportion of ACS. While we have considerable mastery of the biological basis of plaque rupture, and the mechanisms by which lipid- lowering can attenuate this trigger of thrombosis, a striking knowledge gap yawns regarding mechanisms of superficial erosion. This process differs substantially from plaque rupture: human lesions that have provoked erosion generally lack a prominent lipid collection, have few macrophages and more proteoglycan and glycosaminoglycans (GAGs) rather than thin, collagen-poor fibrous caps. Recent clinical data suggest that the management ACS due to erosion, unlike those due to plaque rupture, does not require urgent invasive treatment, rendering the quest for greater understanding of the mechanisms of erosion medically imperative. Our newly published data suggest a role for neutrophils (polymorphonuclear leukocytes, PMN), and neutrophil extracellular traps (NETs) in superficial erosion. We will use a validated experimental preparation in mice that superimposes disturbed flow on a GAG and proteoglycan-rich intima, conditions that pertain to human plaques complicated by superficial erosion, to probe molecular and cellular mechanisms of this type of thrombotic complication of atherosclerosis. My proposal centers on the unified theme of PMN and NET functions. 1) We will test using mice deficient in peptidyl arginine deiminase 4 (PAD4) the hypothesis that at sites of flow disturbance in arteries with erosion-like intimas, NETs participate critically in local endothelial injury and thrombosis. 2) We will test the hypothesis that myeloid-related protein (MRP) 8/14, we have previously implicated in arterial diseases, contributes to local NETosis and in endothelial injury and thrombosis at sites of flow disturbance in arteries with erosion-like intimas. 3) We test the hypothesis that mice bearing in myeloid cells the V617F Jak2 variant associated with clonal hematopoiesis and increased atherosclerotic risk in humans, will have aggravated NETosis and endothelial injury and thrombosis at sites of flow disturbance in arteries with erosion-like intimas. This aim will not only provide mechanistic information regarding superficial erosion, but will help elucidate the mechanism of increased thrombotic events in individuals who bear this somatic mutation common in those with clonal hematopoiesis, a newly recognized potent cardiovascular risk factor. Our studies will also explore novel therapeutic strategies immediately translatable to the clinic.